The increasing level of integration and miniaturization in semiconductor devices such as the dynamic random access memory (DRAM) has brought about a need to change the various metal film materials and metal oxide film materials making up the devices.
In particular, there is a desire for improvements in conductive metal films for multilevel metallization applications in semiconductor devices, and a changeover to high-conductivity copper interconnect lines is underway. To hold down interference between layers of such copper lines, low dielectric constant materials (i.e. low-k materials) are used as the interlayer dielectric material in multilevel metallization. However, one problem that has arisen is that oxygen atoms present within the low-k material are readily taken up by the copper lines, and lowers the conductivity of the lines. Hence, technology to form a barrier film between the low-k material and the copper lines is being studied for the purpose of preventing oxygen migration from the low-k material. Metallic ruthenium films are attracting attention as a material which does not readily take up oxygen from dielectric layers and which can easily be dry etched, and which are thus capable of being used as such barrier films. Metallic ruthenium is also noteworthy as materials capable of fulfilling at the same time both the role of the above-described barrier film and the role of a plating growth film in damascene film formation wherein the copper lines are buried by a plating process.
Moreover, in semiconductor device capacitors as well, on account of their high oxidation resistance and high conductivity, metallic ruthenium films have been attracting attention as electrode materials for high dielectric constant (i.e. high-k) materials such as alumina, tantalum pentoxide, hafnium oxide, and barium strontium titanate (BST).
Up until now, sputtering processes have commonly been used in the formation of such metallic ruthenium films. Recently, however, chemical vapor deposition is being studied as a way to achieve smaller structures, thinner films and greater amenability to mass production.
Yet, the metal films which are commonly formed in chemical vapor deposition, owing to the thin state of aggregation by microcrystals and other reasons, have a poor surface morphology. The use of compounds such as tris(dipivaloylmethanato)ruthenium, ruthenocene, bis(alkylcyclopentadienyl)ruthenium and (cyclohexadienyl)ruthenium tricarbonyl as chemical vapor deposition materials is currently being investigated as a means for solving such problems of morphology (see Patent Documents 1 to 4).
In addition, to prevent the degradation of materials adjoining the metallic ruthenium film during the film-forming step and stabilize the production conditions when the above-described chemical vapor deposition materials are used in a manufacturing operation, it is desired that the materials have a good storage stability. However, when existing compounds such as ruthenocene and bis(alkylcyclopentadienyl)ruthenium are used, the oxidation of adjoining materials and associated deterioration in performance arise in a short time due to the influence of oxygen admixture in the film-forming operation, as a result of which the resulting ruthenium film sometimes has a diminished conductivity. In the case of (cyclohexadienyl)ruthenium tricarbonyl, the film forming operation can be carried out in an inert atmosphere, but the ruthenium material itself sometimes has an inferior storage stability.
The use of bis(acetylacetonato)(1,5-cyclooctadiene)ruthenium as a chemical vapor deposition material has also been investigated (see Patent Document 5). Yet, this compound is a solid at an ordinary temperature and has a low vapor pressure. In order to reduce the design load of the vaporizer in the chemical vapor deposition apparatus, there has been a desire for a lower melting point and a higher vapor pressure.